1. Field of the Invention
In modern internal combustion engines, in particular Diesel engines, injection systems are used in which a high-pressure pump puts the fuel at a high pressure level. The fuel acts on a high-pressure reservoir body (common rail), which when the engine is in operation is constantly under pressure or in other words is subjected to a system pressure level generated by the high-pressure pump. High-pressure lines that ensure the supply of fuel to the engine cylinders branch off from the high-pressure reservoir body. Via fuel injectors, the fuel that is delivered via the high-pressure lines is injected into the combustion chamber of the cylinders of the engine.
2. Description of the Prior Art
In common rail injection systems, the injection event into the combustion chambers of the engine is uncoupled from the pressure generation in the high-pressure reservoir body (common rail). As a result, the instant and quantity of fuel injection can be controlled by engine electronics. This makes an injection adapted to the particular engine load possible. In typical applications, a system pressure of at least 1800 bar is generated in the high-pressure reservoir body (common rail); even high pressures above 2000 bar can be generated. By means of common rail injection systems, a plurality of injections per work cycle can be achieved. Typically, this results in a preinjection, a main injection, and a postinjection.
The control of the injection event is effected with the aid of an electrical signal, which is generated by the control unit of the engine. The electrical signal serves to trigger a solenoid valve for actuating the fuel injector. This solenoid valve, via suitable hydraulics, regulates the motion of a preferably needle-shaped injection valve member, which with its tip opens or closes at least one injection opening into the combustion chamber of the engine. The injection event is initiated by actuation of the solenoid valve, as a result of which a fuel-filled control chamber is pressure-relieved by actuation of the preferably needle-shaped injection valve member. Because of the pressure relief of the control chamber, the preferably needle-shaped injection valve member moves upward, and as a result, at the tip of the injection valve member, injection openings embodied in the nozzle body are opened.
In the prior art, the solenoid valve exists in many different structural forms, as for example in German Patent Disclosure DE 196 50 865 A1. In a variant, a spherically embodied valve element is used, which is disposed at the upper end of the fuel injector and can be moved longitudinally of the fuel injector axis, which coincides with the axis of the injection valve member. In the closed state, the spherically embodied valve element seals off a conically polished valve seat.
As a further variant, the solenoid valve can also be placed in the lower region of the fuel injector, particularly in the injector body of the fuel injector. European Patent Disclosure EP 0 740 068 B1 discloses one such variant of a fuel injector. A valve member there is guided in a valve body, which is sealed off from the fuel that is at high pressure. In this way it is ensured that the fuel at high pressure does not exert any forces on the valve member. Typically, the axis of motion of the valve member, in such a variant, is offset laterally from the axis of motion of the injection valve member. Such a fuel injector is substantially more expensive to produce than a fuel injector provided with a spherically embodied valve member.